Hydroxylamine is prepared commercially by the Raschig process or variations thereof in which ammonium or sodium nitrite are reacted in aqueous solution with ammonium or sodium bi-sulfite and sulfur dioxide and the resulting disulfonate salts are subsequently hydrolyzed to a solution containing essentially hydroxylammonium sulfate, sulfuric acid, ammonium sulfate and/or sodium sulfate plus minor amounts of the corresponding nitrates. This solution can be used, after neutralization with ammonia, as a source of hydroxylamine, e.g. for the synthesis of oximes from ketones. However, there is no simple method for isolating pure hydroxylamine or pure hydroxylammonium salts from the mixture.
One method for obtaining pure hydroxylammonium salts consists of utilizing the hydroxylammonium containing mixture to synthesize an oxime from a ketone, separating the oxime from the spent solution and hydrolyzing this oxime with a strong mineral acid to recover hydroxylammonium salt and the ketone which can be recycled. This method uses long periods of heating for the hydroylsis and requires expensive equipment for the separation of the oxime from the spent solution and of the hydroxylammonium salt from the ketone. Moreover, salts of hydroxylamine with weak or oxidizing acids cannot be prepared by this method because these acids either do not effect hydrolysis of oximes or decompose the hydroxylammonium salt formed during hydrolysis. Salts of such acids can be prepared by neutralizing cold solutions of hydroxylamine with the corresponding acid.
Heinz Holzapfel in Z. Anorg. und Allgem. Chemie, Vol. 288, page 28 (1956) describes the preparation of hydroxylamine from hydroxylammonium salts by employing an anion exchange resin in the OH form. This publication does not relate to the separation of hydroxylamine from solutions containing other cations. As disclosed in U.S. Pat. No. 3,508,864 issued Apr. 28, 1970 to Wallace T. Thompson et al., hydroxylammonium perchlorate can be produced either by liberating hydroxylamine from a hydroxylammonium salt by passage through an anion exchange resin and neutralizing with perchloric acid, or by absorbing hydroxylammonium ion on a cation exchange resin and then passing perchloric acid through the resin. This method does not separate hydroxylamine from other cations. A cation exchange method is described by Earl J. Wheelwright in Industrial Engineering Chemistry Process Design Development, Vol. 16 No. 2 (1977), page 220 for the preparation of hydroxylammonium nitrate. This method does not separate hydroxylamine from other cations and moreover the resulting solution of hydroxylammonium nitrate contains significant amounts of nitric acid.
While the prior art describes methods for the preparation of hydroxylamine and hydroxylammonium salts, there is a need for a simple and inexpensive process for separating hydroxylamine from solutions containing salts of other cations.